Halichondrin B is a large naturally occurring polyether macrolide originally isolated from the marine sponge Halichondria okadai with potent antiproliferative activities.

A total synthesis of Halichondrin B was published in 1992 (Aicher, T. D. et al. , J. Am. Chem. Soc. 114:3162-3164).
Eribulin, a synthetic macrocyclic ketone analogs of halichondrin B with potent antiproliferative activities is an anticancer drug marketed by Eisai Co, under the trade name Halaven and it is also known as E7389, B1939 and ER-086526.

It was first reported in U.S. Pat. No. 6,214,865. Accordingly, new methods for the synthesis of halichondrin B analogs and particularly, eribulin useful as anti-cancer agents are desirable.